A numerical control apparatus performs numerical control processing according to a machining program commanded by a paper tape or the like, and drives a machining apparatus based on the processing result, to machine a workpiece exactly according to the command.
Meanwhile, generally numerical control apparatuses adopt a von Neumann computer configuration using a microprocessor, and the software that controls the system employs a time-sharing control system using a real time operating system. In these systems, because sequential processing programs—hierarchically structured tasks—are executed in a time-sharing manner in a predetermined order, according to interrupt signals (“interrupts”, hereinafter referred to as ITs) every control unit time ΔT (e.g., 10 ms), blanks are occasionally produced in the computing result output when a program being executed is interrupted along the way. These appear in the numerical control apparatus as absent control information on the machine (tool) position, namely, as a phenomenon where null data is output. Although an interruption in most cases does not affect the machined surface, accumulation of interruptions—while being very small amounts of time—contributes to increased cycle time.
Therefore, as a means for resolving the above-described problem, for example, a control system is present as described in the specification of International Publication Number: WO01-44882 A1, in which a specified machining program is converted, in advance before machining operation, with respect to the NC shaft, into control data for positioning, interpolation feeding, or the like according to interpolation data, and is converted, with respect to the main shaft, into control data for performing operations on the main shaft, such as rotation at a commanded rotational frequency, stop, and an orientation operation; and during the machining operation, the servo motor or the main-shaft motor is controlled using the converted data.
However, because the system replaces the machining program with control data for positioning or interpolation feeding according to the interpolation data, there is a problem in that the system cannot respond to cases when an operator desires to change the feed rate by speed override or the like, when the operator desires to change the operation of the machine according to the content of the variable data, or when the operator desires to change the workpiece offset data during the machining operation.
In addition, a problem has been that a plurality of machining programs cannot be converted all at once, and another problem has been that the operator must always perform the conversion operation before the machining operation.